4.1 Variation in hydrochemical parameters
The descriptive statistics of these parameters have been supplied in Table 2 to aid an in-depth analysis of the laboratory data. The ability of water to react with acidic or alkaline compounds in water is measured by its pH (Islam et al., 2017). It is a regulating factor that regulates the types of ions present in water and the balance between carbonate, carbon dioxide, and bicarbonate (Sadat-Noori et al., 2013 ; Hem, 1985). The pH range measured was 6.2 to 7.64, with an average of 7.15 and a skewness of -0.8107. (Table 2). This means that a higher percentage of the water samples were in the pH range of the base. In reality, the water samples were slightly alkaline in 80 percent of the cases. The pH levels in the research region are within the acceptable range (6.5–8.5) and hence indicate that the water is safe to drink (Fig. 3). Total dissolved solutes (TDS) can be used to determine the potability of water on the spot (Sharma et al., 2016). TDS levels in water are determined by the chemical composition of the water and the solubility of the aquifer materials through which it flows. TDS levels are highest in sample site 4 (395 mg/L) and lowest in sample location 11 (32.7 mg/L), with an average of 193.06 mg/L. (Table 2). TDS levels in the study region did not exceed the 500 mg/L maximum allowed limit. Ion exchange, evaporation, sediment dissolving, and rainwater penetration, according to Aghazadeh et al. (2016), can all contribute to high TDS and electrical conductivity (EC). TDS levels in groundwater can potentially be influenced by the application of agrochemicals in large quantities. According to Sharma et al. (2016), excessive levels of groundwater TDS could be caused by dissolved salts from the unsaturated zone. The high amounts of TDS found in the groundwater samples examined should be a cause for alarm. TDS levels beyond a certain threshold have been shown to cause gastrointestinal discomfort and laxative effects (Selvakumar et al., 2014). The potability of the water samples was also assessed using Davis and De Wiest's (1966) classification. Total hardness reduces the capacity of water to lather, resulting in water and detergent waste during laundry (Davis and De Wiest, 1966). The total hardness (TH) of the groundwater samples tested ranged from 40 to 510 mg/L, with a mean of 248.75 mg/L. (Table 2). At 6.25 percent of the examined sample, the hardness value surpasses the maximum permitted limit. The presence of calcium and magnesium bicarbonates, sulfate, and chloride causes hardness. Hard water is normally safe for human consumption, but it can pose major issues in industrial settings, where scum accumulation can cause boilers, cooling towers, and other equipment to fail (Ramya et al., 2015). The spatial distribution of hydrochemical variation within the study area is depicted in Fig. 2.
(a)(b)(c)
(d)(e)(f)
(g)(i)(j)
(k)(l)(m)
Figure 2
Spatial distribution of various groundwater parameters (a) Sulphate, (b) pH, (c) Magnesium, (d) Potassium, (e) Sodium, (f) Total hardness, (g) Nitrate, (i) Fluoride, (j) Chloride, (k) Total dissolved solids (l) Bicarbonate and (m) calcium.
4.2 Cation chemistry
The amounts of key positive ions (Ca2+, Mg2+, Na+ and K+) were measured in order to better understand groundwater hydro-geochemistry. Ca2+ and Mg2+ ions in alkaline earths ranged from 0 to 48 mg/L and 3 to 21 mg/L, respectively, with a mean of 26.75 mg/L and 11.13 mg/L (Table 2). They are both within the permissible limit 75 mg/L and 30 mg/L respectively, as recommended by WHO (2011) and NSDWQ (2015). The concentrations of Na+ and K+ ions varied from 52.8 to 503.25 mg/L (mean value of 197.16 mg/L) and 2.4 to 40 mg/L (mean value of 21.64 mg/L), respectively as shown in (Table 2). The high levels of Na + could be due to erosion of salt deposits from sodium-bearing rocks, groundwater pollution by sewage, and irrigation The sodium concentration in 43.33% of the samples was greater than 200 mg/L. Although the presence of Na + at high concentrations in drinking water poses no major health risk, it can deteriorate soil structure and lower agricultural production if the water is utilized for irrigation (Islam et al., 2017).
4.3 Anion chemistry
The concentrations of main anions were used to examine the hydrochemistry of groundwater (i.e., HCO3−, Cl−, SO42−, NO3− and F−). The concentrations ranged from 28 to 420, 32 to 305, 9 to 175, 1.7 to 132 and 0.13 to 1.16 mg/L, with a mean of 227.56, 119.50, 71.13, 53.70, and 0.53 mg/L, respectively. Major ions in groundwater were found in the following order: HCO3 > Cl > SO4 > NO3 > F for anions, contributing 48.17, 25.30, 15.06, 11.37, and 0.11 percent of the total anion content, respectively. Chloride (Cl−) is a small constituent of the earth's crust (Shanthi et al., 2002); its level was within the maximum permitted limit in 96.67 percent of the samples. However, in the study conducted by Balakrishnan et al. (2011), the chloride content in their samples above the ideal limit of 250 mg/L, indicating that the groundwater may have a perceptible salty taste. Weathering of rock, atmospheric deposition, landfill leachates, septic tank effluents, poor sanitary conditions, chemical fertilizers, and industrial effluents in sewage could all contribute to greater chloride concentrations (Samantara et al., 2017). Sulfate SO4 is found in large amounts in groundwater and does not constitute a health risk at levels found in drinking water. Its increasing content in drinking water, on the other hand, signals declining water quality, which could pose a health risk. The oxidative weathering of sulphide is the most typical source minerals such as pyrite (FeS2). Gypsum and anhydrite, on the other hand, are substantial sulphate sources in water (Han et al., 2013). The NSDWQ guideline threshold for nitrate (NO3−) in drinking water was exceeded in 53.33% of the samples. Excess NO3− in drinking water can cause a variety of problems in children and adults, including methemoglobinemia, stomach cancer, goiter, and hypertension (Mjumdar and Gupta, 2000). The main sources of nitrate contamination include anthropogenic activities such as septic tanks, seepage beds, municipal or domestic sewage, and nitrogenous trash. As a result, multiple studies used a variety of approaches to remove it from groundwater (Qu et al., 2015; Liu et al., 2016; Chu and Wang, 2017). Although fluoride (F−) is a powerful acid (Kale and Pawar, 2017), the content in all groundwater samples is well within the maximum allowed limit, so there is no regional change in its concentration. According to Nawlakhe and Bulusu (1989), lower fluoride concentrations are safe for dental health, but greater fluoride concentrations are hazardous to the spinal cord, skeletal fluorosis, and ligament deformation.
Table 2
Statistical Summary of Parameters
Parameters | Range | Average | SD | Skew | Kurtosis | Median | Maximum NSDWQ | Maximum WHO |
TDS | 32.7–395 | 193.056 | 99.8493 | 0.08709 | -0.3558 | 196.5 | 500ppm | 1000ppm |
pH | 6.2–7.64 | 7.14938 | 0.393 | -0.8107 | 0.50207 | 7.175 | 6.5–8.5 | 6.5–8.5 |
Potassium | 2.4–40 | 21.6438 | 13.8426 | -0.2026 | -1.8575 | 27.5 | 50mg/l | 12mg/l |
Sodium | 52.8–503.25 | 197.163 | 142.301 | 1.14963 | 0.33744 | 152.55 | 200mg/l | 200mg/l |
Bicarbonate | 28–420 | 227.563 | 121.769 | 0.04974 | -1.1057 | 195 | 200mg/l | 200mg/l |
Sulphate | 9–175 | 71.125 | 44.7018 | 0.87194 | 0.43467 | 62 | 100mg/l | 400mg/l |
Chloride | 32–305 | 119.5 | 86.2407 | 1.14944 | 0.33729 | 92.5 | 250mg/l | 250mg/l |
Nitrate | 1.7–132 | 53.695 | 40.0025 | 0.57799 | -0.7091 | 43.8 | 50mg/l | 10mg/l |
Fluorides | 0.13–1.16 | 0.53188 | 0.28138 | 0.73621 | 0.04807 | 0.48 | 1.5mg/l | 1.5mg/l |
Total Hardness | 40–510 | 248.75 | 144.505 | 0.35322 | -0.7862 | 220 | 150mg/l | 500mg/l |
Calcium | 0–48 | 26.75 | 15.3514 | -0.5396 | -0.8379 | 29 | 75mg/L | 200mg/l |
Magnesium | 3–21 | 11.125 | 4.80104 | 0.3541 | -0.0054 | 11.5 | 30mg/l | 50mg/l |
All concentration inn mg/L excluding pH |
4.4 Piper trilinear diagram
The Piper diagram's triangular cationic zone revealed that all of the groundwater samples (100%) fall into the sodium and potassium classes, but the anionic triangle revealed that about 86.67 percent of the samples fall into the bicarbonate zone. The remaining samples in the anion triangle fell into the no dominating zone (10%) and the Cl zone (3.33%), respectively (Figure. 4), with no samples belonging to the sulfate type (strong acidic zone). According to the piper plot (Fig. 4), 86.67% of the samples were of the Na-K-HCO3 type, 13.33% of the samples were of the Na-K-Cl-SO4 type, and 0 percent of the samples were of the Ca-Mg-HCO3 and Ca-Mg-Cl-SO4 kinds. The plot shows that 100% of the samples are of the type Na + K > Ca + Mg (alkalis exceed alkaline earths). As a result, alkaline earth does not surpass alkalis in any sample, and weak acid exceeds strong acid in more than half of the groundwater samples (86.67 percent). According to Magesh et al. (2012), this sort of water has minor salinity concerns and is good for drinking and agriculture. The findings also point to a sodium (Na) dominance, which could be due to rock deterioration (Xiao et al., 2015). Furthermore, as can be seen from the mixed groundwater types, numerous processes contribute to the composition of the hydro-chemical facies. The Piper plot (Fig. 4) also revealed Na+ and K+ dominance in the cation composition, while HCO32− dominates the anion composition in the groundwater samples.
4.5 Gibbs analysis
The Gibbs diagram is commonly used to investigate the link between aquifer lithology and water chemistry (Gibbs, 1970). In this diagram, the functional sources of dissolved chemical elements are split into three distinct fields: precipitation dominance, evaporation dominance, and weathering (Rock dominance) (Krishna-Kumar et al., 2015; Selvakumar et al., 2017). The Gibbs (1970) figure was utilized by Tiwari et al. (2017) and Khan and Jhariya (2018) to analyze the key driving sources regulating groundwater chemistry. The plot of the geochemical data on Gibbs diagrams which is the ratios of\(\frac{Cl}{Cl+HC{O}_{3}}\) and \(\frac{Na}{Na+Ca}\) as a function of TDS suggested rock weathering as a major driving force, with precipitation being a minor influence, thus controlling the groundwater chemistry of the study area (Fig. 5). Majority of the water samples in the study area show rock–water interactions (Fig. 5) and as a result rock weathering is a major driving source for chemical constituents in groundwater in Makurdi metropolis.
4.6 Correlation matrix
Total dissolve solids (TDS) have a significant positive association with Mg2+ (0.56), Cl− (0.322), SO42− (0.765) Ca2+ (0.891), Na+ (0.322), and a moderate correlation with NO3− (0.086), indicating that these ions are primarily supplied from agricultural chemical fertilizers (Selvakumar et al., 2017). (Table 3). Additionally, groundwater components such as Ca2+ (0.859), Mg2+ (0.28), Cl− (0.193), NO3− (0.125) and SO42− (0.729) have a significant positive connection with TH (Table 3). Ca2+ – Mg2+ (0.44), Ca2+ – Cl− (0.294) and Ca2+ – SO42− (0.76) have a good and positive correlation and are primarily obtained from natural processes, such as dissolution and rock–water interaction (weathering) (Tabrez et al., 2022). It means that significant cations and alkaline earth and TDS have a strong relationship. The most important TDS parameters are cations. There were also strong correlations between cation and anion, implying that they are produced from the same geochemical process. WQI values show a strong and substantial relationship with Ca2+ (0.73), SO42− (0.862), Cl− (0.756), K+ (0.73), Na+ (0.756), TH (0.63), HCO3− (0.766), TDS (0.687) and Mg2+ (0.724), as well as a moderate relationship with NO3− (0.554) (Table 3). According to further study, TDS and TH had a significant positive correlation of 0.796 As carbonates dissolve, contaminants in limestone, such as SO42−, Cl−, and SiO2, are exposed to the solvent action of water and enter into solution, according to Das and Nag (2017). This helps to explain why TDS and TH, as well as Ca2+ and SO42− (r = 0.765) and Cl− (r = 0.322), have such a strong association. The dissolution of anhydrite, gypsum, and halite results in a strong correlation coefficient between Na+ and Cl− in groundwater samples, which is often documented in literature (Islam et al., 2017; Li et al., 2013; Giridharan et al., 2009). The high association between Ca2+ and SO42− is the same way.
Table 3
Correlation Matrix of Parameters (n = 60)
| PH | TDS | TH | Ca | Mg | Na | K | HCO3 | Cl | NO3 | SO4 | F | WQI |
PH | 1 | | | | | | | | | | | | |
TDS | 0.418 | 1 | | | | | | | | | | | |
TH | 0.484 | 0.796 | 1 | | | | | | | | | | |
Ca | 0.533 | 0.891 | 0.859 | 1 | | | | | | | | | |
Mg | 0.564 | 0.56 | 0.28 | 0.44 | 1 | | | | | | | | |
Na | 0.562 | 0.322 | 0.193 | 0.293 | 0.537 | 1 | | | | | | | |
K | 0.271 | 0.635 | 0.407 | 0.625 | 0.751 | 0.504 | 1 | | | | | | |
HCO3 | 0.602 | 0.788 | 0.902 | 0.874 | 0.349 | 0.477 | 0.513 | 1 | | | | | |
Cl | 0.562 | 0.322 | 0.193 | 0.294 | 0.537 | 1 | 0.504 | 0.477 | 1 | | | | |
NO3 | 0.176 | 0.086 | 0.125 | 0.244 | 0.3 | 0.201 | 0.334 | 0.173 | 0.201 | 1 | | | |
SO4 | 0.601 | 0.765 | 0.729 | 0.76 | 0.748 | 0.543 | 0.689 | 0.724 | 0.544 | 0.27 | 1 | | |
F | 0.656 | 0.602 | 0.193 | 0.588 | 0.81 | 0.376 | 0.536 | 0.544 | 0.376 | 0.332 | 0.699 | 1 | |
WQI | 0.661 | 0.687 | 0.63 | 0.73 | 0.724 | 0.756 | 0.73 | 0.766 | 0.756 | 0.554 | 0.862 | 0.712 | 1 |
4.7 Water quality index
The Water Quality Index (WQI) divides water into five categories based on hydro-chemical parameters: excellent water (EW), good water (GW), poor water (PW), very poor water (VPW), and unfit for drinking (UDP) (Table 4). The WQI ranges from 24.6 to 112.4, with a mean of 68.02 (Table 2). TDS, TH, Ca2+, Mg2+, Cl−, NO3−, SO4 2− and Na+ all have a positive correlation with WQI. Approximately 15% of groundwater samples are classed as "excellent water" (Table 4). All hydro-geochemical parameters in these groundwater samples are less than or below the NSDWQ's 2015 designated maximum desirable level. Approximately 78% of groundwater samples studied were categorized as 'good water' (Table 4). Hydro-chemical concentrations were compared to excellent water, and all samples are within acceptable and maximum allowable levels. Approximately 7% of the groundwater samples are classed as 'bad drinking water' (Table 4). Groundwater needs to be protected from the use of chemical fertilizers and contamination by agro-based companies. The spatial distribution of the water quality index is shown is Fig. 6.
Table 4
Classification of WQI (after Sahu and Sikdar, 2008; Singh et al., 2016)
WQI range | Category of water | Samples in this category (%) |
< 50 | Excellent water (EW) | 15 |
50–100 | Good water (GW) | 78 |
100–200 | Poor water (PW) | 7 |
200–300 | Very poor water (VPW) | 0 |
> 300 | Unfit for drinking purpose (UDP) | 0 |
Table 5
WQI with category of water
Sample code | Latitude | Longitude | WQI | Category of water |
1 | 7.714583 | 8.5360278 | 90.5 | Good water |
2 | 7.67 | 8.5333611 | 98.3 | Good water |
3 | 7.686278 | 8.5357778 | 111.5 | Poor water |
4 | 7.697361 | 8.5333333 | 106.7 | Poor water |
5 | 7.6925 | 8.5200278 | 37.9 | Excellent water |
6 | 7.720361 | 8.5126944 | 79.5 | Good water |
7 | 7.730278 | 8.5030833 | 70.2 | Good water |
8 | 7.739778 | 8.5094722 | 56.2 | Good water |
9 | 7.725667 | 8.5420278 | 48.3 | Excellent water |
10 | 7.722806 | 8.5553889 | 57.9 | Good water |
11 | 7.716556 | 8.6034722 | 24.6 | Excellent water |
12 | 7.712889 | 8.5785 | 53.8 | Good water |
13 | 7.701472 | 8.5536667 | 54.5 | Good water |
Sample code | Latitude | Longitude | WQI | Category of water |
14 | 7.76125 | 8.5605833 | 112.4 | Poor water |
15 | 7.751611 | 8.5522778 | 35.5 | Excellent water |
16 | 7.7495 | 8.5581389 | 51.9 | Good water |
17 | 7.809921 | 8.530345 | 68.1 | Good water |
18 | 7.757573 | 8.398285 | 69.6 | Good water |
19 | 7.669532 | 8.406613 | 72.1 | Good water |
20 | 7.805757 | 8.441116 | 69.7 | Good water |
21 | 7.826577 | 8.498817 | 66.8 | Good water |
22 | 7.780772 | 8.498223 | 65.8 | Good water |
23 | 7.749244 | 8.527371 | 62.7 | Good water |
24 | 7.682025 | 8.563063 | 73.8 | Good water |
25 | 7.708199 | 8.610057 | 34.6 | Excellent water |
26 | 7.723665 | 8.622549 | 44.3 | Excellent water |
27 | 7.698086 | 8.612437 | 46.4 | Excellent water |
28 | 7.691542 | 8.516901 | 44.6 | Excellent water |
29 | 7.657226 | 8.492735 | 76.9 | Good water |
30 | 7.794045 | 8.499279 | 66.2 | Good water |
31 | 7.626888 | 8.574826 | 73.7 | Good water |
32 | 7.667934 | 8.640856 | 62.1 | Good water |
33 | 7.683488 | 8.539 | 107 | Poor water |
34 | 7.825197 | 8.493753 | 66.7 | Good water |
35 | 7.853037 | 8.550147 | 63.6 | Good water |
36 | 7.821628 | 8.603684 | 63.1 | Good water |
37 | 7.802354 | 8.6251 | 63 | Good water |
38 | 7.796644 | 8.577986 | 67.4 | Good water |
39 | 7.766662 | 8.522307 | 64.5 | Good water |
40 | 7.681716 | 8.575131 | 68 | Good water |
41 | 7.698848 | 8.620103 | 48.7 | Excellent water |
42 | 7.648879 | 8.586552 | 70.7 | Good water |
43 | 7.638885 | 8.546577 | 80.9 | Good water |
44 | 7.586061 | 8.550147 | 74.7 | Good water |
45 | 7.616756 | 8.590122 | 71.3 | Good water |
46 | 7.66958 | 8.618675 | 58.7 | Good water |
47 | 7.653162 | 8.564423 | 77.7 | Good water |
48 | 7.613901 | 8.567993 | 74.9 | Good water |
49 | 7.676719 | 8.488756 | 74 | Good water |
50 | 7.74953 | 8.64937 | 58.7 | Good water |
51 | 7.713436 | 8.429633 | 67.1 | Good water |
52 | 7.612761 | 8.474676 | 77.1 | Good water |
53 | 7.719836 | 8.460994 | 66.7 | Good water |
Sample code | Latitude | Longitude | WQI | Category of water |
54 | 7.622279 | 8.510963 | 78.7 | Good water |
55 | 7.758503 | 8.450287 | 67.5 | Good water |
56 | 7.610381 | 8.446123 | 77.8 | Good water |
57 | 7.606217 | 8.509773 | 79.5 | Good water |
58 | 7.627632 | 8.619228 | 68 | Good water |
59 | 7.565766 | 8.504419 | 79.5 | Good water |
60 | 7.623468 | 8.505014 | 78.4 | Good water |
4.8 Hierarchical cluster analysis (HCA)
HCA was used to find sites that shared a lot of similarities. For 60 groundwater samples in the research location, a dendrogram chart (Fig. 7) was created using Ward's approach (1963) and divided into three clusters. Approximately 91 percent of groundwater samples in clusters I, II, and III are similar to WQI classes PW, GW, and EW, respectively, according to cluster analysis. Some groundwater samples did not belong in the excellent or good water cluster groups. The findings of groundwater study show that the majority of ground samples (47) classed as 2nd cluster 2nd have good water quality, while 3rd cluster has excellent water quality (9) and 1st cluster has low water quality (4). The present studies make it clear that notable spatial analysis results of WQI are statistically significant.